1. Field of the Invention
The present disclosure relates to transfer circuits. More particularly, the present disclosure relates to a circuit topology and method for switching a load between two power converter circuits without interrupting the current to the load during a transfer between the power converters.
2. Description of the Related Art
Power electronic apparatuses for converting electric power from one form to another are referred to as power converters (or power bridges). The power conversion is accomplished using power semiconductor devices. The power semiconductor devices are used as switches. The power semiconductors may include thyristors (also called SCRs, or silicon controlled rectifiers), triacs, power transistors, power MOSFETs, IGBTs (insulated gate bipolar transistors), IGCTs (integrated gate commutated thyristors), and MCTs (MOS-controlled thyristors). Power converters may be generally classified as AC-DC converters, DC-DC converters, and DC-AC converters (i.e., inverters).
To provide redundancy in power conversion circuits and systems, it is necessary to provide a backup circuit and/or components for at least portions of the power conversion circuit and system. For example, in a power generator regulator and an inverting dc drive using an IGBT power converter to regulate power from a source and provide the regulated power to a load, it is known to provide two of the IGBT power converters. Two IGBT power converters are provided, wherein each of the IGBT power converters provide redundant power conversion functionality for the other IGBT power converter in the instance the other IGBT power converter cannot perform its power conversion functionality.
A problem with many known redundant power conversion systems is that the output load must be reduced to zero before the load can be transferred from one power converter to the other (i.e., redundant) power converter. Consequently, the output load current is interrupted during the transfer between the power converters.
The heretofore solution for switching between the power converters without reducing the load current to zero during the switching thereof required a large and expensive DC contactor. The use of the large DC contactor however may necessitate the use of additional circuitry for protecting the contactor contacts and system wiring from an over-voltage situation. High-voltage arcs inside the contactor are particularly problematic with high-inductance loads.
It is also desirable in a number of applications to switch between the power converters after the on-line power converter has failed, without reducing the load current to zero during the switching.
Another problem with prior, known redundant power conversion systems is the coordination required amongst the two power converters to ensure that, in the instance one of the power converters fails and/or becomes disconnected from the source, the failed and/or disconnected power converter does not remain connected to the load during an invoked switching sequence. This is necessary to prevent the other power converter from feeding energy into the failed converter instead of the load. For example, in a system with a high impedance source, the source current may not be high enough to clear the fuses. Therefore, the difficult task of coordinating the fuse(s) to the source impedance is needed.
Thus, there exists a need for a circuit topology and method for switching the load between two power converter circuits without interrupting the current to the load during the transfer between the power converters of the power converter circuit and system.